Yes, ROUSSEAU is a Scrabble word!

Letter values in Scrabble US: R 1, O 1, U 1, S 1, S 1, E 1, A 1, U 1.

Is it a valid word?

ROUSSEAU is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

French philosopher and writer born in Switzerland; believed that the natural goodness of man was warped by society; ideas influenced the French Revolution (1712-1778)
French primitive painter (1844-1910)

Also: jean-jacques rousseau, henri rousseau, le douanier rousseau.